1.我们希望可以做到下面的事情1.1.Ensure that variables exist (i.e., are defined and have non-null values)1.2.Set default values for variables1.3.Catch errors that result from variables not being set1.4.Remo

1.系统内置变量1.1 positional variable:$0,$11.2 two special variables:$@,$*1.3 the variable #1.4 all these variables are read-only .2.自定义变量自定义变量格式:varname=varvalue就可以了,实用的时候$varname.3.局部变量如果你